The present invention relates to phonograph cartridges and more particularly to a replaceable stylus assembly for use in phonograph cartridges.
Phonograph pickup cartridges are generally either of the magnetic or ceramic type. Magnetic cartridges have recognized advantages in fidelity and response characteristics over ceramic cartridges and are widely used in quality high fidelity and stereophonic equipment.
In a magnetic cartridge, a jeweled stylus is used to track the grooves of a record disc. The stylus has attached to it a magnetic member which moves with the stylus within a magnetic circuit. The circuit includes portions about which a voltage generating coil is mounted so that flux variations in the circuit resulting from movement of the magnetic member are reflected in voltage changes at the output of the coils.
Heretofore, magnetic cartridges have been classified as being of either the moving magnet or moving iron type. In the former, typified by U.S. Pat. No. 3,297,831, a permanent magnet moves directly with the jeweled stylus. The latter construction is typified by U.S. Pat. No. 3,546,399 wherein a tubular armature of permeable material moves with the stylus. The armature is magnetically coupled to a fixed permanent magnet which thus serves as the flux source to the magnetic circuit through the armature. In either case, it is important that the magnetic member (i.e., permanent magnet in the first type of cartridge or permeable armature in the latter cartridge) move in faithful correspondence to the jeweled stylus.
Heretofore, it was common practice to support the armature within an elastomeric grommet which in turn was supported within a nonmagnetic tube. To support the grommet in position, the nonmagnetic tube was crimped over the grommet for substantially the entire length of the grommet. Ideally, the elastomeric grommet was to act as a universal joint for the armature. However, because of the nature of the support of the grommet within the nonmagnetic tube, the joint was not truly a universal joint and the mechanical impedance of the system was unduly high thus adversely affecting low frequency responses of such prior art devices.
In view of the above, it is the principal object of the present invention to provide an improved stylus assembly wherein the magnetic member is supported in such a manner as to provide low mechanical impedance so that the magnetic member freely moves in accurate correspondence to the motion of the stylus and thereby provides true and accurate response to variations in the record groove.